1.1. Nitric acid is now made by the oxidation of ammonia. It used to be made from air and water. This process used very large amounts of electricity.

Air was blown through an electric arc and heated to 3000 °C.  

 The equilibrium mixture leaving the arc contained 5% of nitric oxide. This mixture was cooled rapidly. At lower temperatures, nitric oxide will react with oxygen to form nitrogen dioxide. 

 Nitrogen dioxide reacts with oxygen and water to form nitric acid.

 i) Suggest a reason why the yield of nitric oxide in equilibrium 1 increases with temperature.

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 ii) What effect, if any, would increasing the pressure have on the percentage of nitric oxide in equilibrium 1? Explain your answer.

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 iii) Deduce why equilibrium 2 is only carried out at lower temperatures.

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 iv) Complete the equation for the reaction between nitrogen dioxide, water and oxygen to form nitric acid.

 ........NO₂ + O₂ + ............ → ............HNO₃

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 v) Ammonia is more expensive than water and air. Suggest a reason why the ammonia-based process is preferred to the electric arc process.

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1.2. Nitric acid is used to make the fertiliser ammonium nitrate, NH₄NO₃.

 i) What advantage has this fertiliser over another common fertiliser, ammonium sulfate, (NH₄)₂SO₄?

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 ii) Plants need nitrogen to make chlorophyll. Explain why chlorophyll is essential for plant growth.

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